Due to the rising cost of liquid fuel (e.g. diesel fuel) and ever increasing restrictions on exhaust emissions, engine manufacturers have developed dual-fuel engines. An exemplary dual-fuel engine provides injections of a low-cost gaseous fuel (e.g. natural gas) through air intake ports of the engine's cylinders. The gaseous fuel is introduced with clean air that enters through the intake ports and is ignited by liquid fuel that is injected during each combustion cycle. Because a lower-cost gaseous fuel is used together with liquid fuel, cost efficiency may be improved. In addition, the combustion of the gaseous and liquid fuel mixture may result in a reduction of harmful emissions.
In dual-fuel engines, use of a gaseous fuel injector may necessitate inclusion of a gaseous fuel control valve to control the flow of gaseous fuel through a pathway into the combustion chamber. However, operation of the control valve may result in residual gaseous fuel at one or more locations along the gaseous fuel pathway after the control valve closes. This residual gaseous fuel may become undesirable waste or contaminate a subsequent injection event.
One method of handling the difficulties presented by residual gaseous fuel is described in U.S. Pat. No. 5,632,253 (the '253 patent) that issued to Paul et al, on May 27, 1997. The '253 patent describes a combustion system, in which fuel is injected into a combustion chamber through a fuel injection line. Once the fuel flow is cut off, air is injected into the fuel injection line to purge the line of any residual fuel until the combustion chamber is ready for another injection.
Although the system of the '253 patent may address the drawbacks associated with residual fuel located in fuel injection lines, it may not be adequate for all applications. For example, in systems that include a gaseous fuel injector located in an air box, the system may force the residual fuel into the air box, thus contaminating the air supply. Further, the residual fuel that is purged from the fuel injection lines may still become waste, thus reducing the efficiency of the system.
The disclosed purge system is directed to addressing one or more of the problems set forth above and/or other problems of the prior art.